Historical Smalt is glass that has been colored by cobalt. When molten glass contacts water it shatters. This is "Pulverized and ground potassium glass colored blue by cobalt" according to Artiscreation.
Unfortunately this color may darken in an oil painting. There are several different grades of smalt as well as different colors. One deep blue variety is currently called Royal Smalt.
The pigment is rated B for toxicity, so use with caution and use protective gear. We are not health experts but we have heard it is extremely dangerous/hazardous to breathe. Additionally, these pigments contain cobalt. Please see the Artist's Guide to Health and Safety for information about the hazards associated with cobalt pigments in general.
